diff -r 07239de796bb -r e756a8c72c3d cms/drupal/modules/menu/menu.admin.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/cms/drupal/modules/menu/menu.admin.js	Fri Sep 08 12:04:06 2017 +0200
@@ -0,0 +1,46 @@
+(function ($) {
+
+Drupal.behaviors.menuChangeParentItems = {
+  attach: function (context, settings) {
+    $('fieldset#edit-menu input').each(function () {
+      $(this).change(function () {
+        // Update list of available parent menu items.
+        Drupal.menu_update_parent_list();
+      });
+    });
+  }
+};
+
+/**
+ * Function to set the options of the menu parent item dropdown.
+ */
+Drupal.menu_update_parent_list = function () {
+  var values = [];
+
+  $('input:checked', $('fieldset#edit-menu')).each(function () {
+    // Get the names of all checked menus.
+    values.push(Drupal.checkPlain($.trim($(this).val())));
+  });
+
+  var url = Drupal.settings.basePath + 'admin/structure/menu/parents';
+  $.ajax({
+    url: location.protocol + '//' + location.host + url,
+    type: 'POST',
+    data: {'menus[]' : values},
+    dataType: 'json',
+    success: function (options) {
+      // Save key of last selected element.
+      var selected = $('fieldset#edit-menu #edit-menu-parent :selected').val();
+      // Remove all exisiting options from dropdown.
+      $('fieldset#edit-menu #edit-menu-parent').children().remove();
+      // Add new options to dropdown.
+      jQuery.each(options, function(index, value) {
+        $('fieldset#edit-menu #edit-menu-parent').append(
+          $('<option ' + (index == selected ? ' selected="selected"' : '') + '></option>').val(index).text(value)
+        );
+      });
+    }
+  });
+};
+
+})(jQuery);